Regional ion channel gene expression heterogeneity and ventricular fibrillation dynamics in human hearts

RATIONALE: Structural differences between ventricular regions may not be the sole determinant of local ventricular fibrillation (VF) dynamics and molecular remodeling may play a role. OBJECTIVES: To define regional ion channel expression in myopathic hearts compared to normal hearts, and correlate expression to regional VF dynamics. METHODS AND RESULTS: High throughput real-time RT-PCR was used to quantify the expression patterns of 84 ion-channel, calcium cycling, connexin and related gene transcripts from sites in the LV, septum, and RV in 8 patients undergoing transplantation. An additional eight non-diseased donor human hearts served as controls. To relate local ion channel expression change to VF dynamics localized VF mapping was performed on the explanted myopathic hearts right adjacent to sampled regions. Compared to non-diseased ventricles, significant differences (p<0.05) were identified in the expression of 23 genes in the myopathic LV and 32 genes in the myopathic RV. Within the myopathic hearts significant regional (LV vs septum vs RV) expression differences were observed for 13 subunits: Nav1.1, Cx43, Ca3.1, Cavalpha2delta2, Cavbeta2, HCN2, Na/K ATPase-1, CASQ1, CASQ2, RYR2, Kir2.3, Kir3.4, SUR2 (p<0.05). In a subset of genes we demonstrated differences in protein expression between control and myopathic hearts, which were concordant with the mRNA expression profiles for these genes. Variability in the expression of Cx43, hERG, Na(+)/K(+) ATPase ss1 and Kir2.1 correlated to variability in local VF dynamics (p<0.001). To better understand the contribution of multiple ion channel changes on VF frequency, simulations of a human myocyte model were conducted. These simulations demonstrated the complex nature by which VF dynamics are regulated when multi-channel changes are occurring simultaneously, compared to known linear relationships. CONCLUSIONS: Ion channel expression profile in myopathic human hearts is significantly altered compared to normal hearts. Multi-channel ion changes influence VF dynamic in a complex manner not predicted by known single channel linear relationships

Variable Nav1.5 Protein Expression from the Wild-Type Allele Correlates with the Penetrance of Cardiac Conduction Disease in the Scn5a+/− Mouse Model

BACKGROUND: Loss-of-function mutations in SCN5A, the gene encoding Na(v)1.5 Na+ channel, are associated with inherited cardiac conduction defects and Brugada syndrome, which both exhibit variable phenotypic penetrance of conduction defects. We investigated the mechanisms of this heterogeneity in a mouse model with heterozygous targeted disruption of Scn5a (Scn5a(+/-) mice) and compared our results to those obtained in patients with loss-of-function mutations in SCN5A. METHODOLOGY/PRINCIPAL FINDINGS: Based on ECG, 10-week-old Scn5a(+/-) mice were divided into 2 subgroups, one displaying severe ventricular conduction defects (QRS interval>18 ms) and one a mild phenotype (QRS53 weeks), ajmaline effect was larger in the severely affected subgroup. These data matched the clinical observations on patients with SCN5A loss-of-function mutations with either severe or mild conduction defects. Ventricular tachycardia developed in 5/10 old severely affected Scn5a(+/-) mice but not in mildly affected ones. Correspondingly, symptomatic SCN5A-mutated Brugada patients had more severe conduction defects than asymptomatic patients. Old severely affected Scn5a(+/-) mice but not mildly affected ones showed extensive cardiac fibrosis. Mildly affected Scn5a(+/-) mice had similar Na(v)1.5 mRNA but higher Na(v)1.5 protein expression, and moderately larger I(Na) current than severely affected Scn5a(+/-) mice. As a consequence, action potential upstroke velocity was more decreased in severely affected Scn5a(+/-) mice than in mildly affected ones. CONCLUSIONS: Scn5a(+/-) mice show similar phenotypic heterogeneity as SCN5A-mutated patients. In Scn5a(+/-) mice, phenotype severity correlates with wild-type Na(v)1.5 protein expression

Remodelage de l'expression des canaux ioniques cardiaques (rôle dans le phénotype électrophysiologique )

Les approches gène à gène ont montré que les cellules cardiaques sont capables d'adapter leurs propriétés électrophysiologiques à des contraintes externes physiologiques ou pathologiques, en modifiant l'expression transcriptionnelle de leurs canaux ioniques. Cependant, elles n ont fourni que des données partielles. La génomique autorise aujourd hui un abord global de ce remodelage. Au cours de ma thèse j ai utilisé des outils de génomique afin de définir l ensemble des canaux ioniques cardiaques dont la régulation transcriptionnelle était modifiée face à des contraintes externes. J ai d une part évalué la distribution des transcrits des canaux dans différentes régions du cœur humain sain et sa modulation en fonction du sexe. D autre part, j ai analysé le remodelage ionique associé à la fibrillation auriculaire, au syndrome de Brugada et à l insuffisance cardiaque. J ai pu ainsi montrer que cette régulation transcriptionnelle est systématique, qu elle concerne un grand nombre de canaux et notamment leurs sous-unités régulatrices, et enfin qu elle est généralement cohérente avec les propriétés électrophysiologiques des cellules cardiaques. On peut donc supposer que ces cellules utilisent de façon préférentielle la transcription des canaux pour adapter leurs propriétés électrophysiologiques. Il reste maintenant à définir quels sont les facteurs de transcription impliqués dans la régulation des canaux et quels sont les mécanismes de rétrocontrôle qui existent entre le phénotype électrophysiologique des cellules cardiaques et leur machinerie de transcription.Gene by gene approaches have shown that cardiac cells adapt their electrophysiological properties to physiological or pathological situations by modifying gene expression levels of ion channels. However, these approaches have only provided partial data. Today, genomics allows to investigate this remodeling in a global way. During my thesis I used genomic tools to determine which ion channels have a modified transcriptional regulation when exposed to external pressure. First, the distribution of ion channel gene expression in different regions of the human heart, and its modulation by gender, was evaluated. Secondly, ionic remodeling associated with atrial fibrillation, Brugada syndrome and heart failure was analyzed. Thus, I showed that transcriptional regulation of ion channels is systematic, that it concerns a large number of ion channels and particularly auxiliary sub-units, and finally that it is generally consistent with the electrophysiological properties of the cardiac cells. We therefore suggest that cells preferentially use ion channel transcription to adapt their electrophysiological properties. We have now to determine which transcription factors are implicated in channel regulation and what are the feed-back mechanisms between the electrophysiological phenotype of the cardiac cells and their transcription machinery.NANTES-BU Médecine pharmacie (441092101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Chronic heart rate reduction remodels ion channel transcripts in the mouse sinoatrial node but not in the ventricle

International audienc